It has long since been known to use conveyors to transport large numbers of heavy automobile components over very long distances in order to move them to work stations. These conveyors can be overhead conveyors or can be positioned on the ground depending on the operations to be carried out on the products.
The conveyors consist of a rail, a drive chain and trolleys. The rail often has an I-shaped section and forms the path to be followed by the components to be conveyed. A drive unit drives the chain, which is connected to the trolleys, themselves transporting the products. The drive unit must be capable of pulling a total load the weight of which varies, e.g. from one hundred to three thousand kilograms.
The trolley for its part consists of two wheels and two arms and a wedge the thickness of which allows the ends of the two arms to be held in position inside a link of the chain. The arms of the trolleys support the load which is suspended from the rail in the case of an overhead conveyor or rests on the rail in the case of a conveyor positioned on the ground.
Each arm of the trolley is provided at its end with a wheel pivoted by means of a ball bearing, the wheels bearing against the rail on either side thereof.
All of the elements making up the conveyor, i.e. the rail, trolley and chain, are made of steel, thereby creating considerable at the work site, as the different elements of the conveyor are constantly subjected to tensile or compressive stresses, shocks and friction between the steel elements, thereby amplifying the already high decibels given the noise of the production machines and the drive motors of the chain of the conveyor.
These noises due to shocks and friction of the trolleys with the rail and the chain are highly amplified by the fact that the rail is of quite a considerable length, reaching, on average, one hundred to one thousand metres per conveyor, and that the number of trolleys positioned on the rail is also high as the trolleys are spaced apart at an average distance of three hundred to one thousand millimeters.
With this level of noise, it is therefore common to find employees complaining of hearing problems and headaches.
As the products are moved, those directed by the rail follow a variable path consisting of a series of turns, straight lines, slopes and gradients and are also subjected to a series of acceleration and deceleration operations depending on whether or not the components are situated in a work zone. To this end, the wheels in contact with the rail are subjected to tensile and compressive stresses which cause considerable friction and shocks of the wheels on the rail, both made of steel, and therefore considerable wear of the two elements.
The wheels in contact with the rail must therefore be lubricated in order to reduce this wear and stoppages of the production line in order to repair certain elements of the conveyor. This lubrication is in addition effected in a considerable quantity given the kilometers of conveyor found on the work site.
However, in spite of this lubrication, the rail is still subject to considerable wear, which can reach approximately one centimeter after a few years, meaning that the rails generally have to be changed every four to five years at the vertical and horizontal curves.
During the operation of the conveyor, the arms of the trolleys are also subjected to tensile and compressive stresses as the chain works on the ends of the arms, thereby causing shocks of the wheels on the rail and in the chain and thus further increasing the noise and wear of the elements of the conveyor.
In addition, the moving chain under tension is subjected to considerable friction at the pins and links, which thus wear out very rapidly, meaning that the chain has to be changed frequently and the chain lubricated liberally. An average of two hundred liters of lubricating oil is therefore used per month for approximately five or six conveyors several kilometers in length.
Some conveyors on the work site are situated in a humid environment which in time shocks and wear, leading to corrosion spreading to the work site and, more precisely to the products to be conveyed. This is the reason that, corrosion spots are often found on car bodies when the latter are painted.
In addition, this corrosion and the liberal lubrication of the conveyor take place on site, i.e. on the products, making the working conditions and environment very unpleasant.
This invention aims to obviate all of these disadvantages and one of the objects is to reduce the noise, lubrication and wear of the conveyor by using a trolley made of composite material, designed to withstand tensile and compressive stresses and to limit shocks onto the wheels on the rail and at the chain.
Therefore, one advantage of this invention is that it reduces shocks and friction of the wheels on the rail of the conveyor by absorbing the stresses applied to the wheel in the event of variations in course and variations in speed.
The rail and the wheel are thus subject to virtually no wear and lubrication of the wheels at the rail can be dispensed with completely.
Another advantage of this invention is that it is possible to increase and vary the speed and the conveying of the components in the "dead zones", i.e. where there is no work to be carried out on the products, by virtue of the absorption of stresses on the wheel, as the wheels in contact with the rail have the advantage that they are deformed easily in the event of a variation in speed and direction and can thus withstand stresses and shocks so that the speed of displacement of the trolleys can be increased in the zones where there is no work to be carried out on the components.
This invention also uses arms made of composite material with a particular structure to withstand tensile and compressive stresses and thereby dampen shocks of the wheels on the rail and shocks on the drive chain. This also reduces the noise and wear of the elements of the conveyor.
The reduction of all shocks and the use of composite material for the wheel and the arm virtually eliminates noise during operation. The noise is thus reduced by ten decibels compared to existing conveyors with elements made of steel.
Another advantage of this invention is that it reduces the weight of the conveyor by using trolleys made of composite material instead of steel. This reduction in weight reduces the tensile stresses on the chain, thereby extending its service life, and also allows for the use of smaller drive units as the load to be pulled is smaller.
Another advantage of this invention, combined with the reduction in tensile stresses and shocks of the chain, is to reduce the wear of the chain and, more particularly, of the pins and links of the chain by increasing the mechanical properties of the pins.
This therefore increases the service life of the chain and the quantity of lubricating oil and the frequency of lubrication of the latter can be reduced, thus making it easier to control the maintenance operations of the facility.
Other objects and advantages of this invention will be clear from the following description given purely by way of a non-limiting example.